Classifications

• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F1/00—Treatment of water, waste water, or sewage
  • C02F1/02—Treatment of water, waste water, or sewage by heating
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D1/00—Evaporating
  • B01D1/26—Multiple-effect evaporating
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
  • C01G28/00—Compounds of arsenic
  • C01G28/005—Oxides; Hydroxides; Oxyacids
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
  • C01P2004/00—Particle morphology
  • C01P2004/60—Particles characterised by their size
  • C01P2004/61—Micrometer sized, i.e. from 1-100 micrometer
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
  • C01P2006/00—Physical properties of inorganic compounds
  • C01P2006/80—Compositional purity
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F1/00—Treatment of water, waste water, or sewage
  • C02F1/52—Treatment of water, waste water, or sewage by flocculation or precipitation of suspended impurities
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F1/00—Treatment of water, waste water, or sewage
  • C02F1/66—Treatment of water, waste water, or sewage by neutralisation; pH adjustment
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F2101/00—Nature of the contaminant
  • C02F2101/10—Inorganic compounds
  • C02F2101/103—Arsenic compounds
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F2103/00—Nature of the water, waste water, sewage or sludge to be treated
  • C02F2103/18—Nature of the water, waste water, sewage or sludge to be treated from the purification of gaseous effluents
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10S210/00—Liquid purification or separation
  • Y10S210/902—Materials removed
  • Y10S210/911—Cumulative poison
  • Y10S210/912—Heavy metal

Definitions

• the present invention relates, in general, to the recovery of arsenic containing residues from acidic aqueous solution, and, more particularly, to the recovery of arsenic values from acidic gas wash solutions, for example, acidic gas wash solutions produced in the pyrometallurgy of copper sulfide ores.
• arsenic present in the copper ore often remains in the refined products and/or in the process wastewater.
• arsenic-containing residues present significant cost and operational challenges to the copper recovery process as the residues must be treated or disposed of as hazardous materials to avoid negatively impacting the environment. Therefore, plants and/or refineries producing copper concentrates and products containing more than 5% arsenic must generally pre-treat these concentrates to remove arsenic .
• a conventional process for pre-treating an arsenic- containing copper concentrate or product comprises heating the concentrate or product under reducing conditions to volatilize the arsenic as a sulfide.
• the arsenic sulfide is then combusted with air to produce arsenic trioxide and sulphur dioxide as follows:
• the resulting calcinated material typically has an arsenic content ranging within commercial standards .
• arsenic-containing copper concentrates are smelted and reduced in converters or flash- type ovens to volatilize arsenic and produce an arsenic- containing off-gas.
• the arsenic-containing off-gas is further treated in a gas washing plant to recover the arsenic.
• the arsenic-containing off-gas is contacted with an acid to generate an effluent in the form of an acid solution.
• the acidic gas wash effluent is then neutralized with lime, filtered and dried to produce a calcium arsenate sludge.
• Kohno et al. in U.S. Patent No. 4,588,564, describe a process for removing arsenic from the exhaust gas of a sulfide ore smelter.
• the process discloses scrubbing the exhaust gas with water at a predetermined concentration and temperature to provide an effluent solution having an arsenic concentration of at least 80% of its saturation concentration.
• the solution is then filtered and arsenic trioxide is crystallized under vacuum or by cooling at a pH less than 2.
• the arsenic trioxide crystals are contacted with hydrochloric acid to produce an arsenic trioxide product .
• Tomita, et al . in J. Metal. Vol. 35, No.
• Yen in U.S. Patent No. 5,338,460, describes the removal of dissolved heavy metals, including arsenic, from aqueous solutions, particularly industrial and mining waters.
• the procedure discloses reacting the dissolved heavy metal with an inorganic sulfide or hydrosulfide at high temperature between 0° and 100°C and controlling the pH between 2 and 3.5.
• Allgulin in U.S. Patent No. 4,566,975, describes treating aqueous solutions containing impure heavy metals such as arsenic, phosphorus and mercury.
• the reference describes precipitating impure heavy metals from solution in two stages, using sodium hydroxide and ferric sulfate as precipitating agents.
• Arsenic impurities are then recovered as a sludge of iron-arsenic oxide, which can be stabilized and disposed.
• the present invention is directed to a process for recovering arsenic from an aqueous acid solution.
• the process comprises heating the acid solution in one or more evaporators in series to concentrate the solution.
• the concentrated solution is then cooled to crystallize arsenic as arsenic trioxide.
• the crystallized solution is filtered to produce a solid phase comprising impure arsenic trioxide crystals, which are purified to produce a purified crystal product comprising arsenic trioxide.
• the present invention is further directed to a process for recovering arsenic from an aqueous acid solution.
• the process comprises concentrating the acid solution in one or more evaporators in series to produce a concentrated acid solution.
• the concentrated acid solution is cooled to crystallize arsenic as arsenic trioxide and the crystallized solution is filtered to produce a solid phase of impure arsenic trioxide crystals and a residual liquid phase.
• the solid phase of impure crystals is purified to produce a purified crystal product comprising arsenic trioxide while the residual liquid phase is contacted with sodium sulfide for the further recovery of arsenic.
• Arsenic is precipitated in the residual liquid phase as an arsenic sulfide and the precipitated residual liquid phase is filtered to produce an arsenic sulfide product and a purified liquid phase containing less than about 5 ppm arsenic.
• the present invention is directed to a process for continuously processing effluents of an aqueous acid solution containing arsenic.
• the process comprises filtering the acid solution to eliminate suspended solids before evaporating and concentrating the solution in a chain of evaporators in series at low pressure to produce a concentrated acid solution.
• Arsenic in the concentrated acid solution is crystallized as arsenic trioxide by cooling and the crystallized solution is filtered to produce a solid phase comprising impure arsenic trioxide crystals and a residual liquid phase.
• the solid phase is purified by sublimating arsenic trioxide from the solid phase, thereby producing a purified gaseous phase and a solid sublimation residue.
• the purified gaseous phase is immediately cooled to produce a purified crystal product comprising arsenic trioxide .while the residual liquid phase is processed for the further recovery of arsenic.
• the residual liquid phase is contacted with sodium sulfide to produce an arsenic sulfide precipitate, which is filtered from the residual liquid phase to produce a solid phase comprising arsenic sulfide and a purified liquid phase comprising a weak sulfuric acid containing less than 5 ppm arsenic.
• the solid phase comprising impure arsenic trioxide crystals is purified by lixiviation.
• the process comprises contacting the solid phase comprising impure arsenic trioxide crystals with sodium hydroxide to lixiviate arsenic trioxide and produce a purified liquid phase comprising arsenic trioxide and a solid phase comprising a lixiviation solid residue.
• the purified liquid phase is separated from the lixiviation solid residue and contacted with an acid, thus lowering the pH to less than 10 and crystallizing arsenic trioxide.
• the crystallized liquid phase is then filtered to produce a purified crystal product comprising arsenic trioxide.
• FIG. 1 is a block flow diagram illustrating one embodiment of the present invention
• FIG. 2 is a process flow diagram illustrating a preferred embodiment of the present invention.
• FIG. 2A is a continuation of the process flow diagram of FIG. 2 illustrating a preferred embodiment of the present invention.
• the present invention comprises a process for recovering arsenic, in the form of a commercially salable arsenic trioxide product, from an acidic gas wash effluent produced in the pyrometallurgy of copper sulfide ores .
• the present invention is suitable for use in recovering arsenic from any acidic aqueous solution containing from about 1 to about 20 g/L of arsenic and from about 25 to about 150 g/L of acid.
• the solution may also contain a wide variety of other impurities, for example, metals and/or halogens, without adverse effect on the process of the present invention.
• the raw material acid solution for the process of the present invention comprises the effluent from a gas wash tower operated in the conventional pyrometallurgy of copper sulfide.
• the effluent generally comprises from about
• the process of the present invention generally comprises heating the solution to evaporate water and concentrate arsenic.
• the arsenic concentration of the acid solution is increased to an equilibrium concentration (i.e., saturation concentration) by heating the solution in one or more evaporators in series.
• an equilibrium concentration i.e., saturation concentration
• one skilled in the art can readily determine an appropriate saturation or equilibrium concentration for arsenic at a particular temperature. It is important to note that the saturation concentration should be determined at the temperature of crystallization rather than the solution temperature during evaporation.
• the saturation concentration (i.e., the minimum concentration for crystallization) of arsenic is between about 5 and about
• the solution is evaporated and concentrated in one or more evaporators in series operating at a temperature ranging from about 70°C to about 120°C.
• the process of the present invention comprises four evaporators in series, wherein the acid solution feed stream originally containing from about 20 to about 150 g/L of arsenic-containing acid is evaporated and concentrated to an acid concentration of from about 200 to about 640 g/L.
• the concentrated liquid mass exiting the last evaporator typically will have a temperature ranging from about 50° to about 70°C, preferably about 60 °C.
• the concentrated solution may be transferred to a thermally insulated storage tank to preserve the temperature of the solution prior to crystallization.
• the concentrated solution may pass directly to a crystallization stage wherein the concentrated solution is cooled to a temperature of from about 0° to about 25°C, more preferably from about 10° to about 20°C to crystallize arsenic in the form of arsenic trioxide crystals.
• the concentrated solution is cooled in one or more crystallizers in series.
• the crystallizers are water-cooled wherein the concentrated solution is contacted with water having a temperature of from about 0° to about 25°C.
• the concentrated solution is cooled to produce a crude arsenic trioxide product comprising impure arsenic trioxide.
• the aqueous acid solution comprises a gas wash effluent produced in the pyrometallurgy of copper sulfide ores
• the impure arsenic trioxide crystals typically contain impurities such as Cu, Fe, Ni, and Ca salts.
• the crystallizer (s) preferably recover at least about 90%, more preferably at least about 95% of the arsenic present in the acidic feed solution. From the crystallizers, the crude arsenic trioxide product is washed and separated in a water-washed filter wherein the crystals are collected for further purification and the remaining liquids are further processed for the removal of any remaining trace amounts of arsenic.
• the collected crude arsenic product is purified to obtain a substantially pure, commercially salable arsenic trioxide product comprising at least about 97% arsenic trioxide, preferably at least about 98% arsenic trioxide, and more preferably at least about 99% arsenic trioxide, most preferably from about 99.8% to 99.9% arsenic trioxide.
• the impure arsenic trioxide crystals are transferred to a sublimation oven wherein the crystals are heated to a temperature sufficient to sublime arsenic trioxide.
• Arsenic trioxide sublimes from the crude arsenic trioxide solid product to form a purified gaseous product comprising arsenic trioxide and a sublimation solid residue.
• the temperature is sufficient to sublime arsenic trioxide from the impure arsenic trioxide crystals without removing a substantial amount of the metal salt impurities to the purified gaseous phase.
• the purified gas phase is removed from the sublimation oven and immediately cooled to form a purified solid product comprising arsenic trioxide crystals having an arsenic trioxide concentration of at least about 99%, more preferably about 99.8 to about 99.9%.
• the sublimation solid residue which typically contains copper sulfides and calcium sulfate, is removed from the sublimation oven and returned to the smelting plant for the further recovery of copper.
• the purified gaseous product may be cooled by any means known in the art for forming arsenic trioxide crystals from a vapor.
• the arsenic-containing vapor is contacted with water jets to cool the vapor and produce purified arsenic trioxide crystals.
• the arsenic-containing vapor is contacted with a cold wall wherein the vapor is cooled to form the purified arsenic trioxide solid product.
• the impure arsenic trioxide crystals undergo alkaline lixiviation to remove impurities.
• the lixiviation process comprises contacting the impure crystals with an alkaline lixiviant such as an alkaline metal hydroxide to remove arsenic trioxide as a purified liquid phase from the crystals.
• the lixiviant is preferably selected to avoid transferring impurities to the liquid phase (i.e., substantially no impurities are lixiviated to the purified liquid phase) .
• the purified liquid phase is then separated from the solids and the solid residue is returned to the smelting plant for further recovery of copper.
• the purified liquid phase is contacted with an acid to adjust the pH to less than 10, which also crystallizes arsenic trioxide.
• the purified liquid is crystallized with sulfuric acid, preferably a solution comprising 98% sulfuric acid, to produce a purified arsenic trioxide product comprising at least about 99% arsenic trioxide, and more preferably about 99.8 to about 99.9% arsenic trioxide.
• the purified arsenic trioxide product can then be collected by means of a filter with the liquid phase being recycled to the lixiviation stage.
• liquids separated from the crude arsenic trioxide product can be further processed to remove arsenic and/or prepare additional recoverable products.
• the filtrate from the crystallization of the crude arsenic trioxide product is collected in a storage tank along with the condensed liquids from the upper part of the evaporator (s) to form a residual arsenic solution.
• the residual arsenic solution is then contacted with sodium sulfide to produce an arsenic polysulfide product (e.g., arsenic trisulfide) which can be recovered from solution as a precipitate.
• the reactions corresponding to the generation and precipitation of arsenic polysulphides are as follows : 2NaHS + H 2 0 Na 2 S + H 2 S (Na 2 S preparation)
• sodium sulfide should be introduced to the residual solution in an amount sufficient to provide a mass ratio of sodium sulfide to arsenic of about 1:4 to about 1:8 in the residual solution.
• an amount of sodium sulfide is introduced into the residual solution to provide a mass ratio of sodium sulfide to arsenic of about 1:6 in order to precipitate arsenic polysulfides from the residual arsenic solution.
• the predominant arsenic polysulfide species formed is arsenic trisulfide along with iron and copper sulfide byproducts.
• the precipitated arsenic polysulfides are recovered by filtration and the remaining liquid, having an arsenic content of less than about 5 ppm, can be transferred to a storage tank for reuse or disposal .
• a feed stream comprising an aqueous arsenic-containing acid solution is introduced into the process of the present invention via pipe 1.
• the solution is first filtered in a dust filter 2.
• the filtered feed stream is transferred to tank 3 before being sent to a first evaporator 5.
• the evaporator 5 comprises a forced circulation type evaporator with a separate, external heat exchanger 6.
• a preferred apparatus of the invention comprises four evaporators in series each with a corresponding heat exchanger for concentrating the feed solution.
• the solution in the evaporation stages, shows incipient formation of arsenic trioxide crystals.
• the concentrated solution is then transferred to a storage tank 9, which is thermally insulated to preserve the temperature of the solution and prevent premature crystallization of arsenic trioxide. From tank 9, the concentrated solution is cooled in a first crystallizer 11 followed by a second crystallizer 13, both of which are cooled with water to form a crude arsenic trioxide product .
• the mass of crystals exiting from crystallizer 13 as the crude arsenic trioxide product is transferred to filter 15, and washed with water.
• the impure arsenic trioxide crystals then fall via conduit 17 to a conveyor belt 19, and through a channel to dump carts 21.
• the loaded dump carts 21 go to a sublimation oven 23. In the sublimation oven, the crude arsenic trioxide product is heated to volatilize arsenic trioxide and form a purified gaseous product.
• the purified gaseous product passes from the sublimation oven to a Venturi-type condenser 27, wherein the purified gaseous product is cooled by means of a pressurized water jet to produce a solution pregnant with purified arsenic trioxide crystals, which is then further cooled in crystallizer 31.
• the dump carts 29 exiting the oven typically contain by-products such as copper sulfate and calcium sulfate, which are returned to the smelting plant for further processing.
• the solution pregnant with pure arsenic trioxide crystals is driven to filter 33 and washed with water to separate a substantially pure arsenic trioxide product having an arsenic trioxide concentration of about 99.8% to about 99.9%.
• Conveyor belt 35 carries the purified product to drying oven 37, and then to storage 39 and packing facility 41, for sale and shipping.
• Filtrate separated from the crude arsenic trioxide product at filter 15 is collected in a storage tank 45 along with the collected condensed vapors from the upper part of the evaporators 5 to form a residual arsenic solution.
• the residual arsenic solution is then passed to the arsenic sulfide precipitation plant for the further recovery of arsenic.
• the residual arsenic solution is transferred to mixing tank 47 and contacted with sodium sulfide from reaction tank 51.
• the sodium sulfide prepared in reaction tank 51 is the reaction product of sodium sulfhydrate and water.
• the reaction in mixing tank 47 forms a reaction mixture comprising arsenic polysulfide precipitates and hydrogen sulfide gas as a byproduct.
• the byproduct hydrogen sulfide gas is passed to a treatment tank 49 and contacted with sodium hydroxide to form water which may be recycled for use as a water source in reaction tank 51.
• the remaining reaction mixture is transferred to filter 51 wherein an arsenic polysulfide solid product comprising arsenic trisulfide is collected on conveyor belt 53 for storage in hopper 55.
• the remaining process liquids separated in filter 51 which contain less than about 1 to about 5 ppm of arsenic, are transferred to holding tank 57 for further use or disposal.
• This example demonstrates the evaporation and concentration of an arsenic solution followed by crystallization and filtration to recover commercial grade arsenic .
• the experiment was begun by heating a solution (2000 cc) containing copper (0.63 g/L), iron (0.107 g/L), arsenic (9.406 g/L) and antimony (0.036) .
• the solution was heated to reduce the volume to 250 cc .
• samples of the solution were collected when the volume was reduced to 1000 cc.
• the solution had an arsenic concentration of 18.45 g/liter and 1.92% of the of the original arsenic content had precipitated.
• the solution had an arsenic concentration of 46.66 g/liter, and 50.65% of the initial arsenic content precipitated or crystallized.
• This example demonstrates the recovery of arsenic from the gas-washing effluent of a sulfuric acid plant.
• the experiment was conducted by heating a solution (1,144 L) obtained from a gas-washing tower of a sulfuric acid plant in sequential stages.
• the solution contained arsenic (11.602 g/L) and sulfuric acid (49.9 g/L).
• the solution was heated in sequential stages to a reduced volume of 96.5 liter.
• the solution was then cooled to 10°C, which caused arsenic trioxide to crystallize. Analysis of the crystals indicated that the crystals contained 97.5% arsenic, which is commercial quality.
• the solution was then treated with sodium sulfide to further recover arsenic. After the addition of sodium sulfide, the solution contained about 580 g/L sulfuric acid with less than 5 ppm arsenic. Thus, the solution could be used as a weak acid in other processes

Landscapes

• Chemical & Material Sciences (AREA)
• Organic Chemistry (AREA)
• Environmental & Geological Engineering (AREA)
• Life Sciences & Earth Sciences (AREA)
• Water Supply & Treatment (AREA)
• Engineering & Computer Science (AREA)
• Hydrology & Water Resources (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Inorganic Chemistry (AREA)
• Removal Of Specific Substances (AREA)
• Inorganic Compounds Of Heavy Metals (AREA)
• Heat Treatment Of Water, Waste Water Or Sewage (AREA)
• Manufacture And Refinement Of Metals (AREA)
• Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
• Vaporization, Distillation, Condensation, Sublimation, And Cold Traps (AREA)

Applications Claiming Priority (5)

Publications (1)

Family

ID=25739108

Family Applications (1)

Country Status (7)

Families Citing this family (15)

Family Cites Families (15)

• 2001
  • 2001-12-14 US US10/381,566 patent/US7232554B2/en not_active Expired - Fee Related
  • 2001-12-14 JP JP2002549588A patent/JP4223809B2/ja not_active Expired - Lifetime
  • 2001-12-14 AU AU2002222360A patent/AU2002222360A1/en not_active Abandoned
  • 2001-12-14 WO PCT/IB2001/002494 patent/WO2002048046A2/en active Application Filing
  • 2001-12-14 EP EP01270498A patent/EP1341723A2/de not_active Withdrawn
  • 2001-12-14 CA CA2431403A patent/CA2431403C/en not_active Expired - Lifetime
• 2003
  • 2003-06-04 ZA ZA200304385A patent/ZA200304385B/en unknown

Non-Patent Citations (1)

Also Published As

Similar Documents

Legal Events